Design and optimization of the secondary circuit for the WCLL BB option of the EU-DEMO power plant

EU-DEMO will be a DEMOnstration Fusion power plant designed to demonstrate production of grid electricity from fusion at the level of a few hundred MW. The Primary Heat Transfer System (PHTS) transfers heat from the breeding blanket (BB), divertor and vacuum vessel to the secondary Power Conversion System (PCS) responsible for conversion of thermal energy into electricity. Two main BB conceptions, and the relative PHTSs, for EUDEMO are being developed: the Helium Cooled Pebble Bed (HCPB) BB and the Water Cooled Lithium Lead (WCLL) BB. Two options for each conception are considered: with or without the Intermediate Heat Transfer System (IHTS), containing the Energy Storage System (ESS), between the BB PHTS and PCS. The role of IHTS+ ESS is to ensure continuous smooth thermal energy transfer from the reactor sources to PCS despite the pulsed operation of the DEMO reactor. In the present work we discuss the mature concept of the PCS configuration for the option WCLL BB with the IHTS+ESS (based on the 2018 EU-DEMO reference), which allows almost constant production of electricity during both plasma pulse and dwell phases. The operating parameters of the circuit were optimized to minimize the temperature oscillations delta T = |Tpulse - Tdwell| in all the circuit components, which occur due to the pulsation of the DEMO cold sources of Divertor and Vacuum Vessel whose HXs are integrated in PCS itself. Operation of the PCS circuit during the pulse and dwell phases was simulated using the GateCycle software, to show the system performance and to enable discussion on the feasibility of the concept.